Abstract
The process of oxygen chemisorption on coal in the temperature range ≈150–300 °C was studied under different experimental conditions using TG-DSC apparatus. As changing experimental conditions, oxygen flow (20 or 200 cm3 min−1), material of crucible (α-Al2O3 or Pt–Rh alloy), and initial sample mass (2–13 mg) were examined with respect to reliability and reproducibility of the parameters derived from TA curves. As parameters quantifying coal oxidation, temperatures of minimal T min and maximal T max sample mass, mass changes (mass loss W H below T min and mass increase W O above T min), heat evolution during oxygen chemisorption Q O (related to the coal mass increase), and kinetic parameters (activation energy E and frequency factor A) were evaluated. Values of T max, E, and A were found to lie in very close intervals independently on experimental conditions (95% confidence intervals were T max = 270.2 ± 0.7 °C, E = 81 ± 3 kJ mol−1, log10 A = 5.9 ± 0.3 s−1). Thus, these parameters can be used as actual characteristics of oxygen chemisorption stage of coal oxidation irrespective on conditions of TA measurements. Opposite, parameter Q O was confirmed to depend clearly on initial sample mass. The dependence is different for crucible materials used; however, it tends to the same value (≈50 kJ g−1) with increasing sample mass. Further, precision of values W H, W O, and T min determined from TG was found to be poor. This fact complicates evaluation of the effect of experimental conditions. Finally, the effect of oxygen flow on all above parameters was found to be negligible. Its influence (if any) was hidden by common experimental errors.
Similar content being viewed by others
References
Kök MV. Temperature-controlled combustion and kinetics of different rank coal samples. J Therm Anal Cal. 2005;79:175–80.
Ozbas KE, Kök MV, Hicyilmaz C. DSC study of the combustion properties of Turkish coals. J Therm Anal Cal. 2003;71:849–56.
Kök MV. An investigation into the combustion curves of lignites. J Therm Anal Cal. 2001;64:1319–23.
Oreshko WF. On the oxidation of coals with different degree of metamorphosis. Izvest Akad Nauk SSSR, Otdel Tekh Nauk. 1951;7:1031–40. (in Russian).
Wang H, Dlugogorski BZ, Kennedy EM. Coal oxidation at low temperatures: oxygen consumption, oxidation products, reaction mechanism and kinetic modeling. Prog Energy Combust Sci. 2003;29:487–513.
Sen R, Srivastava SK, Singh MM. Aerial oxidation of coal-analytical methods, instrumental techniques and test methods: A survey. Indian J Chem Technol. 2009;16:103–35.
Kök MV. Recent developments in the application of thermal analysis techniques in fossil fuels. J Therm Anal Cal. 2008;91:763–73.
Li XR, Koseki H, Iwata Y. A study on spontaneous ignition of bituminous coal. Thermal Sci. 2009;13:105–12.
Ceylan K, Karaca H, Önal Y. Thermogravimetric analysis of pretreated Turkish lignites. Fuel. 1999;78:1109–16.
Feng B, Bhatia SK. On the validity of thermogravimetric determination of carbon gasification kinetics. Chem Eng Sci. 2002;57:2907–20.
Slovák V. Determination of kinetic parameters by direct non-linear regression from TG curves. Thermochim Acta. 2001;372:175–82.
Koga N, Šesták J. Kinetic compensation effect as a mathematical consequence of the exponential rate-constant. Thermochim Acta. 1991;182:201–8.
Koga N, Šesták J. Further aspects of the kinetic compensation effect. J Therm Anal Cal. 1991;37:1103–8.
Jones JC, Henderson KP, Littlefair J, Rennie S. Kinetic parameters of oxidation of coals by heat-release measurement and their relevance to self-heating tests. Fuel. 1998;77:19–22.
Taraba B, Čáp K. Investigations of coal substance by gas chromatography. Uhlí. 1985;33:278–80. (in Czech).
Slovák V, Taraba B. The effect of gas flow and granularity on the chemisorption stage of coal oxidation. Chem listy. 2008;102:742. (in Czech).
Acknowledgements
This study was supported by Czech Science Foundation, project No. 105/06/0630.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Slovák, V., Taraba, B. Effect of experimental conditions on parameters derived from TG-DSC measurements of low-temperature oxidation of coal. J Therm Anal Calorim 101, 641–646 (2010). https://doi.org/10.1007/s10973-010-0878-6
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10973-010-0878-6